1. Field of the Invention
This invention relates generally to a dilutor/dispenser system for reliably dispensing precise predetermined volumes of successive liquid samples.
2. Description of Prior Art
A variety of different systems has been developed for analyzing liquid samples. Each such system requires that a predetermined volume of sample, which may be diluted, be reacted with a precise volume of reagent, to produce a reaction product indicative of the concentration of a particular constituent being analyzed. Present-day systems are classified as being of the continuous- or discrete-type. A continuous-type system has been described, for example, in U.S. Pat. No. 3,241,432, issued on Mar. 22, 1966 and assigned to a common assignee. In such a system, samples are successively introduced as a flowing stream into the system by means of an aspirating probe. Such samples are divided into a plurality of aliquots. The sample aliquots are directed, in phase, along individual conduits, wherein each is appropriately diluted and mixed with one or more selected reagents, in online fashion, so as to be reacted with respect to a particular constituent. The reacted sample aliquots are passed through appropriate reaction detectors, such as colorimeters for color-sensitive reactions, etc., and the analytical results are subsequently recorded in correlated fashion. In such systems, proper sample volumes are ensured by precisely controlling the rate and duration of the sample aspiration. In a discrete- or batch-type system, such as described in U.S. Pat. No. 3,971,630, issued on July 27, 1976 and assigned to a same assignee as the present invention, measured volumes of sample (appropriately diluted) and appropriate reagents, to effect a particular reaction, are introduced into an individual reaction cell. The reaction mixture is then analyzed, e.g., colorimetrically either in the reaction cell or by flowing the reaction mixture through an appropriate reaction detector. Regardless of the system type, it is essential for obtaining accurate results that a proper volumetric ratio be maintained between the liquids being reacted, so that the concentration of the particular constituent being analyzed can be properly related to an absolute standard. Any variation in such ratio, obviously, would not allow proper relating of the analytical results with such standard.
The present invention is particularly intended for use in systems of the discrete-type, wherein the sample is not aspirated directly into the system. In such systems, sample introduction and dilution are usually effected by a dilutor/dispenser unit, which is a liquid-delivery instrument capable of precisely dispensing small sample volumes, appropriately diluted. The probe of the dilutor/dispenser unit is immersed into a sample receptacle, often hand-held by the technician, to aspirate a predetermined sample volume into the probe, against a volume of diluent. Subsequently, the aspirated sample volume, along with a predetermined volume of a diluent, are dispensed into a reaction cell, which may contain or subsequently receive a predetermined volume of reagent to support a particular reaction.
The dilutor/dispenser unit is usually pre-set to aspirate a predetermined volume of sample and, also, to dispense a predetermined volume of diluent. During the aspiration, or sample-loading cycle, a "short" sample can result, which may be unnoticed by the technician. Such "short" sample can result, for example, from the malfunction of the aspirating pump, momentary and unintentional withdrawal of the aspirating probe from the sample liquid, a clogging of the probe inlet, etc.
3. Objects of the Invention
An object of this invention is to provide improved method and apparatus for dispensing precise liquid volumes. Another object of this invention is to provide improved dispenser apparatus which operates to provide a visual indication or an alarm automatically upon aspiration of an improper liquid volume, i.e., a "short" sample. A still further object of this invention is to provide a dilutor/dispenser apparatus which is reliable in operation and suitable for unattended operation.